In serial input/output communications, single or multiple retimer device(s) are often used to extend the reach of a communication link. As serial bit data rates increase, challenging signal integrity requirements and complicated protocols lead to a need for more complex buffering (retimer) devices, which in turn require increased levels of configuration. Certain protocols use in-line speed negotiation and equalization link training, and current industry buffering/retiming solutions regularly fail to properly handle this complicated link up flow, especially when devices are cascaded together. Previous industry solutions are not robust or are not compliant with nor defined by the specification.
There currently is no industry specification dictating how these retimer devices should perform their link up process for most protocols using link training. Therefore there is no standard way, and many of the current implementations do not account for some of the intricacies of adaptive equalization link establishment, especially in a cascaded configuration.